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Showing posts from March, 2014

Completed ALU

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Following my last post on the completed backplane I'm now in a position to connect all the other completed cards together to test the full ALU. The ALU is made up of the logic, arithmetic and control cards and here's how those cards look when plugged in to the backplane:
... and when viewed from the top and back ...
... and finally here's the four cards laid out side by side:
Surprisingly enough with everything connected together it all appears to work OK with only one small exception ... I was finding that the carry out from the arithmetic card wasn't being received by the control card. After much digging around with a multimeter I found the problem wasn't the backplane as suspected but rather that the required wiring had been missed out on the arithmetic card. With the addition of the missing wire link the carry out function was restored. However, this then highlighted a slight design flaw in that the carry out line is passed out to the control bus even when the …

ALU Construction: Completed Backplane

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In my last post I mentioned I'd suffered a bit of a set back with the construction of the ALU backplane. Well, the short version of things is that I've admitted defeat and constructed a new backplane using a different design ... it looks like this:
This design uses stackable headers instead of regular sockets so that the pins extend out of the back of the card far enough to attach an IDC connector. Each of these connectors can then be 'daisy chained' together with ribbon cable making construction relatively quick and easy to do.

So, what went wrong with the original backplane? Well, it was one of those cases where it worked fine on paper and in my head but not quite so in reality. This is where the original card ended up:
In this design the regular sockets have header pins soldered alongside on the back of the card. The idea was that I could then take a length of wire and wrap it around each post soldering as I go. It dawned on me, as I made a start on the wiring, that…

Enclosure Initial Construction

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I've been promising this post for quite a while now ... an update on how the enclosure construction is going. Well, it's very good thanks :)

Firstly, here's a quick reminder of the SketchUp design showing how the enclosure should look:
... and here's how it looks, so far, in reality ...
This is the main frame of the card enclosure and you can see it forms four compartments that will hold five cards each plus backplanes. At the moment the front and back doors are incomplete as they're waiting for the perspex/acrylic sheet (3mm smoked transparent) to be cut. Likewise the perspex that fits in the sides of the main frame are also pending. Because of this the frame as it appears above isn't fully screwed together yet ... the back bars (which kind of form a shape like two 'E's back to back) are just held in by friction on the corners. Once the side perspex panels are in then everything can be screwed together and a very rigid strong frame results. All the jo…

ALU Construction: Completed Control Card Full Test

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The ALU Control Card is now complete and looks like this:
This card was, on the whole, much simpler and quicker to put together than previous cards (despite me initially messing up the zero detection relay positions). As the card isn't too busy I've arranged the wiring away from the empty part of the card so there's room for future expansion or modifications if needed in the future. Not entirely sure what they'd actually be but you never know.

As is now customary when I've completed a card I've created a video replete with voiceover track attempting to demonstrate the card in action and explain what's going on. Here it is:


The completion of the control card actually represents a bit of a mini-milestone ... combined with the logic and arithmetic cards I now have a potentially fully functional ALU. I say potentially because I don't actually have any physical way of connecting the three cards together yet and so my next task will be to complete the card ba…

ALU Construction: Control Card Power Rails & Wire Wrap

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I've been a bit short of time lately so I've been working on the ALU Control Card in little bursts ... but after lots of these little bursts I've now got all the power rails and wire wrap done for this card.

Here's the card as it currently stands:
... and this is how the power rails look on the solder side of the card ...
With the rails and wire wrap all done the card just needs the relays popping in and it should be ready for a test drive.

ALU Construction: Control Card Header Pins & Relay Sockets

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Following on from the first two successfully completed ALU cards, for logic and arithmetic, it's time to make a start on the control card (well, actually, the LEDs and connectors are already done from earlier but you get the gist). The control card performs three functions: control registers, function decoding and zero detection ... and thankfully this card is much simpler than the previous two in terms of relay count and sheer amount of soldering so should come together relatively quickly.

So, I'll start with some pictures of progress so far:
Looking at the first picture the sockets for the zero detect relays are down the left hand side of the card, for the function decoder bottom left and condition registers down the bottom right.

Unfortunately I've made a right royal balls up with the zero detect relay sockets ... apparently unable to read my own diagrams I've mis-aligned the sockets. Each socket should be positioned so that one of the normally-closed switches of on…

Enclosure Disclosure

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Sorry, I will try to rain in the terrible punning post titles.

This time I wanted to share the thoughts and ideas I've been having around building a case to hold my computer when it's eventually complete. I wanted to use a material that would be easy to handle and work with but also one that would produce a nice looking result. I was initially drawn to using wood or possibly even laser cut plywood but in the end I settled on aluminium profile as its sturdy, easy to assemble and, I think, looks really great. In addition to this it's available in a large variety of sizes, shapes and there's plenty of fixtures and fittings available for it.

If you haven't come across it before, aluminium profile is basically created by extruding aluminium through a die to produce bars of varying lengths. The clever thing is that the dies are shaped so that channels are produced that can fit bolts or screws to allow profile to be joined together or for fittings to be attached. Also, t…